The present invention relates to radiant tube heating systems and, in particular, to such a system which incorporates catalytic combustion and air preheating capabilities.
Radiant tube heating systems are used primarily for heat treating various fluids and materials, usually in a controlled ambient such as an inert gas or a vacuum. For example, Kendall et al U.S. Pat. No. 4,204,829 discloses a catalytic combustion tube heating system which provides radiant heating of a fluid heat sink, such as water, for extraction of the energy at an external heat exchanger.
However, to our knowledge, gas-fired radiant tube combustors employing high temperature heterogeneous catalytic combustion have not existed previously. Such a gas-fired radiant tube would be useful in many industrial process heating furnace applications. Presently, industrial process heating furnaces may typically employ conventional gas burners which fire into one end of a tube and, in particular, electric resistance elements, as sources of radiant heat. The electric resistance elements provide certain desirable operating characteristics including high temperatures (2,000.degree. F. and above), precise temperature control and relatively high firing rates (Btu/hr).
A gas-fired radiant tube employing high temperature heterogeneous catalytic combustion would be highly desirable for such industrial process heating furnaces and other similar applications because of potential catalytic combustion advantages such as low emissions levels and uniform radiant energy transfer. However application of such gas-fired radiant tube combustors imposes the requirements of high combustion efficiency and high system thermal efficiency in addition to those of uniform radiant energy transfer and low emission levels.
To our knowledge, the radiant tube heating technology has not previously had available a simple catalytic combustion radiant tube heating system which efficiently satisfies the above requirements.